The present invention relates to a method and apparatus for defect inspection to detect a small pattern defect, a foreign substance, etc. from the difference between the images of an inspected object using light and a reference, and especially to a method and apparatus for inspecting optically the defect of a semiconductor device, a photo mask, a liquid crystal, etc.
In manufacturing of a semiconductor device, a substrate (wafer) is processed by hundreds of manufacturing processes, and a semiconductor device is formed therewith. In each process, a foreign substance may adhere on the substrate (wafer) or a pattern defect may be produced by variation in manufacturing process, which are causes for producing a semiconductor device with inferior characteristics. In the defect inspection system of a semiconductor device, the needs for a classification are growing of various kinds of DOI (Defect Of Interest) and defection of a defect not to be wanted to detect, as well as detection of smaller defects or foreign substances with progress of fine pattern forming process. In order to meet such needs, plural defect inspection apparatuses equipped with optical imaging systems and image processing systems (hereafter called a probe head) are developed, manufactured and on the market in recent years, aiming at the increase in detectable kinds of defect and the improvement in defect detecting performance by using the detection signal in each optical imaging system. These defect inspection apparatuses are actually used in the semiconductor production line.
After the completion of processes such as a lithography, a film forming process, and an etching process, etc. the defect inspection apparatus for a semiconductor device inspects the substrate surface to defect or a foreign substance generated in the processes, and issues an instruction to clean the apparatus used in the process and prevents inferior goods to be otherwise generated by delivering a substrate with a fatal defect to the following process by detecting a defect at an early stage.
In the middle of formation process of a semiconductor device with a substrate, the substrate is loaded to the defect inspection apparatus. The surface of the substrate (wafer) is imaged in the middle of formation of a semiconductor device, and based on the images thus obtained, a defect determination processing is performed by utilizing a defect signal decision threshold disclosed in JP-A-2003-83907, 2003-98113, and 2003-271927, etc., a defect determination is made and the number defects etc. on the substrate are outputted.
When the number defects Nt detected is less than the threshold Nc of defect set up beforehand, the substrate is send to the next process as it is. When the detected defective number Nt is large, the propriety of the substrate reproduction is decided after issuing the cleaning implementation instruction to a previous process device. When the substrate is decided to be refreshable, after washing the substrate in a washing process, this inspection process is applied again, and then sent to the next process.
The substrate (wafer) in the middle of formation of a semiconductor device is an inspected object having the same pattern of portions 1 and 1′ regularly in a line as shown in FIG. 4 (hereafter called a die). The defect inspection method and defect inspection apparatus of the present invention is to compare the images of adjacent dies at the same position in the corresponding coordinates in the dies, respectively, and decide a defective detection based on the differences between the two.
However, if a whole scanning system vibrates or inclines when a stage scanning, a gap will arise in the image formation position of a optical imaging system, making unable to obtain the signals from the same corresponding part of dies for every die opening. This is the major cause of a misalignment of the images between adjacent dies.
An inspection apparatus with plural probe heads is proposed and developed in recent years, and has been applied to a semiconductor production line.
In an optical inspection apparatus with such plural probe heads, a probe head must be installed so that the heads may not interfere with one another. For this reason a case arises where it is difficult to give object lenses the same numerical aperture and some object lenses have to be designed to have smaller apertures, resulting in lower optical resolving power with the system. Accordingly, misalignment calculation accuracy falls when carrying out image misalignment calculation between reference image and inspection image as the preceding step of calculating the difference image between dies. And falling down of the misalignment calculation accuracy causes a decrease in the calculation accuracy of a difference image, and resulting in deterioration of the defect detecting performance.